Top Circuits Page 20
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Using one current source for tbe charge and discharge path in this circuit ensures identical rise and fall times at the capacitor terminal. A Darlington pair ensures identical biasing of the IC during the charge and discharge cycles. The period of the....
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When configured as a free-running multivibrator, a 555 timer provides no more than a 50% duty cycle. By adding two transistors, however, you can obtain a variable 5 to 95% duty cycle without changing the sum of the on and off times. When VouT decreases,....
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The timer circuit shown gives independent control of the output"s on and off intervals, which can range from 0.055 seconds to 30 minutes, relatively unaffected by power-line transients. IC1 is a CMOS programmable-timer chip that includes 24 ripple-binary....
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When used as a stand-alone device, ZN1034E from Ferranti can provide timed intervals ranging from 1 second to 19 days, although the rc time constant is only 220 seconds. The ZN1034E includes an internal voltage regulator, an oscillator, and a 12-stage....
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This simple circuit consists of only two timing components Rr and Cr, the NE555, and bypass capacitor C2. While not essentiaHor operation, C2 is recommended for noise immunity. During standby, the trigger input terminal is held higher than 1/3 Vee and the....
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When Sl is off, Cl charges to within 0.5 V of the battery voltage through diode Dl and resistor R4. When Sl is closed, tbe anode of tbe PUT rises to the positive supply voltage. The PUT does not conduct, because battery voltage appears in series with tbe....
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This timer can be inserted in a power line to provide a controllable delay before a load is energized. The mains voltag..
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This circuit prevents making transmissions that are too long, which "time out" repeaters and/or tie up a communicatio..
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Using an RC oscillator, an up to 24-stage ripple counter O) 16777216 or 2U, and a 0.1-Hz count-rate with #..
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By using an RC oscillator and a programmable divider, this counter can run for hours. An interval osc..
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The watchdog timer contains a counter, IC3, in addition to the usual retriggerable 555 timer, ICl. The counter will so..
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LEDs indicate at a glance what the status of the circuit is at any given moment. Once the reset switch, SI, makes contact,..
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Transistor Ql and resistors Rl, R2, and R3 form a constant current source and the charge current might be adjusted..
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This circuit operates in the astable mode and at the end of the first period (up to several minutes), it produces a tone. ..
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This circuit adapts a frequency counter to measure intervals. It was originally used as a shutter speed checker for a photo application. The watch ticks are clipped and shaped and formed into a square wave. This square wave is used to gate an accurately....
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The first amplifier circuit is a bird phone. In this circuit, the electret mike (MIC1) is mounted in the neck of a large plastic funnel. The amplifier, built around an MC34119 (which is available from D.C. Electronics, P.O. Box 3203, Scottsdale, AZ....
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A diode, such as a IN4148, has a typical -2m V/C temperature coefficient at a 1 mA diode current. Ql and Q2 form a constant current source. D1 is the temperature sensor. ICl-a and -b are dc amplifiers, with ICl-c a temperature reference voltage supply.....
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This timer circuit uses a 555 IC timer and three 74LS193 counters to drive an LED display. SI is activated by one person, who turns on piezo buzzer BZ1 via Ql and also starts the clock; SI is activated by the other person being timed. ..
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The circuit is built around a 555 oscillator/ timer. The circuit provides two time periods. The long-running time period is adjustable from about 1 to 10 minutes, and the short time period is preset to about three seconds. Here`s how the dual timer....
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With switch SI in the off position, as shown, battery voltage is applied across timing-capacitor CI, which stays charged while the rest of the circuitry has no power supplied to it. ..
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The time base is first selected with Sl set for seconds or minutes, then units 0-99 are selected on the two thumbwheel switches S4 and S5. Finally, switch S2 is depressed to start the timer. Simultaneously, the quartz crystal-controlled divider circuits....
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When power is first applied to the circuit, 02 begins to charge via LED1, R3, and R4. When the voltage across C2 reaches Ul`s input trigger level, the output of Ul at pin 6 goes positive for a period that is determined by the values of and it! r That turns....
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The circuit shown in Fig. 62-15A is designed to drive a 15-V, two-phase, bipolar stepping motor, providing a bidirectional single level voltage across each winding at currents of up to 9.6 A. The circuit consists of two identical transistor bridge stages....
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A 4017 decade counter/divider driven from a low-frequency oscillator (Ul-a and Ul-b) is used to drive transistor switches to sequence the windings, as is needed. MOT1 is a 12-V stepper motor. R9 and RIO are selected for the motor`s current rating. A 3.3-Hz....
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The Tesla coil described here can.generate 25,000 V. So, even though the output current is low, be very careful! The main component is a flyback transformer from a discarded TV. A new primary windin_g is needed. Begin by winding 5 turns of #18 wire on the....
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Power is fed to transformer Tl, a small neon-sign transformer, which steps the voltage up to about 3000 Vac. The stepped-up output of Tl is fed through L1 and L2 and across Cl, causing the capacitor to charge until enough power is stored in the unit to....
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This circuit is built around two chips: the MC1458 dual op amp, configured as a preamplifier, and the LM378 dual4-watt amplifier. The gain of the preamp is given by R3/R1 for one side and R4/R2 for the other side, which is about 100. That gain can be....
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On most FM tuners, the stereo indicator lights upon detection of the 19-kHz pilot tone. However, this doesn"t mean that the program is actually stereophonic, since the pilot tone is often transmitted with mono programs also. A similar situation exists on....
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The Stereo Power Meter is made up of two identical circuits and a power supply. Each circuit contains Jwo LM3914 display chips which contain 10 voltage comparators, a 10-step voltage divider, a referencevoltage source, and a mode-select circuit that....
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A simple method of deriving a center or third channel without the use of an extra transformer or ampli..
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When this circuit is connected to a filter and an oscilloscope, the scope displays the filter"s frequency response. A..
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A block diagram of the stereo-TV decoder is shown in A. It shows the overall relationships between the separate sections of the circuit; through show the details of each subsection. The decoder section centers around TCI, a standard 4.5-MHz audio....
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In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
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Receiver. Output from the transducer is amplified by Ql and Q2, and rectified by Dl. Voltage on pin 2 of ICl will go more negative as the input signal increases. ICl is used as a comparator and checks the voltage on pin 2 (i the sound level), to that on pin....
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Low-intensity ultrasonic sound waves in the 30-45 kHz frequency band repel insects and small rodents. The unit is designed to generate a swept square wave from 30 to 45 kHz. The LM555 IC is wired as an ultrasonic oscillator driving a piezoelectric speaker of....
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The device emits ultrasonic sound waves that sweep between 65,000 and 25,000 hertz. Designed around a 556 dual timer, one half operated as an astable multivibrator with an adjustable frequency of 1 to 3 Hz. The second half is also operated as an astable....
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Combine an electrostatic transducer with an ultrasonic transceiver IC to build a ranging system that senses objects at distances from 4 inches to more than 30 feet. Transducer Yl "s broadband characteristic simplifies tuning. The secondary of T1 resonates....
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The 4046 PPL is used as the heart of a tunable ultrasonic receiver that can be used to locate unheard ultrasonic sounds. The receiver might also be used, along with a simple ultrasonic generator, to send and receive Morse code. The incoming ultrasonic....
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This circuit is a 555 timer IC connected as a square-wave generator. Its base frequency is approximately 45kHz, as detennined by the values of Rl, R2, and Cl. The 45-kHz carrier is frequency modulated by a modified trapizoidal voltage waveform applied to....
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The Class A series resonant inverter portrayed is well-known and respected for its high efficiency, low cost, and small size, provided that operating frequency is greater than about 3 kHz. ..
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without significant added complexity, and a natural tendency to run away under no-load (high Q) conditions. The 20-kHz control circuit (see Fig. 2) overcomes these shortcomings hy feeding back into the asymmetrical thyristor trigger pulse generators (see....
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The LM1812 is a complete ultrasonic transceiver on a chip designed for use in a variety of pulse-echo ranging applications. The chip operates by transmitting a burst of oscillations with a transducer, then using the same transducer to listen for a return....
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This submersible sonar positioning apparatus generally consists of dual-opposed ultrasonic transducers, alternately excited, with return signals processed and displayed for observation and measurement. Typical transmitter frequencies range from 50 to....
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Variable width pulses with fast rise times are provided by Ul, and MC34060 operating at 120kHz, the optimum frequency for heating aluminum alloy containers. The pulse width is modulated by sensing the temperature of the target with a thermistor, using its....
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The piezo speaker, MICl, picks up the incoming ultrasonic signal and feeds it to the base of Ql. The two-transistor booster amplifier, Ql and Q2, raises the signal to a level that is sufficient to drive one input of this most unusual mixer circuit.....
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IC2 forms a stable oscillator whose frequency and pulse width is determined by the values of R4, R5, R6, and C4. R4 is made adjustable for precise frequency setting. The output of IC2 is pin 3, which is capacitively coupled to the base of Ql. Ll acts as a....
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This circuit consists of two basic parts: an oscillator tuned to 40kHz, and a voltage doubler with pulse generator. The pulses are about 10 ms long and occur 2-3 per s to reduce battery drain and increase the annoyance factor for a cat, dog, hedgehog, etc. ..
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This circuit uses two transistors and one IC (555 timer IC) to produce a pulsating ultrasonic frequency. Transistors Ql and Q2 are connected in a direct-coupled oscillator. The frequency of that oscillator is set by capacitor CI. The oscillator output is....
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The circuit consists of a multivibrator (Ql & Q2), and a low power output stage Q3. The speaker should have an impedance in the region of 40 to 80 ohms. To use a low impedance speaker, connect an output transformer from the emitter of Q3 to ground. Cl and C2....
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This circuit mimics the dual-tone drone sound that"s produced by the unusual wind instrument. Urnjunction transistors Ql and Q2 are connected in similar audio-oscillator circuits. Each of the oscillator frequencies is determined by one of the two resistors....
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This siren provides a constant audio output, but alternates between two separate tones. The LM13080 is set to oscillate at one basic frequency; ..
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Unijunction transistors Ql and Q2 are both connected as relaxation-type, sawtooth oscillators. Transistor Ql is the low-frequency control oscillator and Q2 is the tone generator. Sawtooth waveforms are produced at the emitter terminals. Without R4....
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Transistors Ql and Q2, with feedback provided via Cl from the collector of Ql to the base of Q2, forms a voltage-controlled oscillator (VCO). De- pending on the voltage applied to Q2 "s base, the VCO frequency ranges from around 60 Hz to 7.5 kHz. The....
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A low-frequency, op-amp oscillator and a VCO, both configured from a single MC3405 ~dual op amp and dual comparator, are tbe major components in a siren circuit tbat can be made to produce various warbles and wails, or serve as an audio sweep generator. ..
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Six preset controls and seven selector switches enable a vast range of different sounds to be produced and altered at will. Such sounds as steam trains chuffing, helicopters flying, bird chirping, and machine guns firing are possible, as well as the usual....
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A pair of timer IC"s are the heart of a circuit that simulates the warbling bee-haw of a British police siren. One of the 555 timers, U2, is wired as an astable multivibrator operating at about 900 Hz. The other, Ul, operates at approximately 1 Hz. Its....
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The wailing sound of a siren is generated by a VFO consisting of Q1 and Q2. Capacitor C2 provides the feedback for the oscillator. The frequency of the oscillator is varied by the voltage applied to the base of Q1 through R3. When switch S1 is closed,....
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The simple circuit transforms the steady beep of an audible-signal device, such as a Mallory sonalert, into a distinctive warble or chirp. The value of R, C2 determines just what tone color you"ll get. With 1k the 1-I"F value shown, the circuit produces....
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This circuit uses one of the LM389 transistors.to gate the power amplifier on and off by applying the muting technique. The other transistors form a cross-coupled multivibrator circuit that controls the rate of the square-wave oscillator. ..
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The oscillator based on IC2 is responsible for producing the sound. Its output is connected to the base of TRl, ..
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This circuit uses a CMOS chip and a VMOS FET amplifier for 6 W of audio output. 18 W of audio can be generated using ..
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A two-tone generator that is alternately switched ON provides a high/low output as might be heard from a traffic vehicle like a police car or ambulance. IC1, CD4011, quad 2-input NAND gate is a two-tone oscillator in which each side, pins 1 through 7 and 8....
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The transmitter keyboard is arranged as a scanned matrix. The matrix consists of 7 driver outputs and 7 sense inputs. The driver outputs DRVON to DRV6N are open-drain n-channel transistors and they are conductive in the stand-by mode. The 7 sense inputs....
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The device generates an adjustable frequency of low to medium powered IR pulses of invisible energy and must be treated with care. The portable battery pack is stepped up to 200 to 300 volts by the inverter circuit consisting of Ql, Q2, and Tl. Ql conducts....
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The circuit is designed to operate at 25 kHz. The data stream turns the 2N4401 hard on or off depending upon the coded state. This in turn switches the series infrared LEDs on and off. The receiver circuit consists of a three stage amplifier with photo....
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This circuit provides a means of detecting the presence of anything by the reflection of infra-red light and provides a direct digital output of object detection. By the use of modulation and high power bursts of infra-red at a very low duty cycle, a....
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Although theIR region is free from radio interference, it is subject to interference from incandescent lamps, fluorescent lamps, stray reflections, and other sources. A simple way to overcome that problem is to create a carrier by chopping the IR radiation....
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When long ranges must be worked with IR light sources, and when high system reliability is required, pulsed-mode operation of the IRis required. Additional reliability of operation is attained by synchronously detecting the photodetector current, as this....
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Infrared emissions detected by Ql are fed through Ula to Ulb, which amplifies the signal by a factor of 100. The amplified output ofUlb is fed to Ulc through R9, C2, and R6. Potentiometer R9 serves as a volume control. With R9 set to pass the maximum....
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The transmitter consists of an oscillator which drives a high output IR emitting diode. The oscillator is a sJire start multivibrator circuit that provides an output of 15 to 1000 mark to space ratio at a frequency of 1 kHz. This large mark to space ratio....
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Gates U1a and U1b are configured as a low-frequency oscillator. The output waveform at pin 11 is nonsymmetrical with the positive portion of the signal, making up only 20% of the time period. Diode D1, a 1N914 general-purpose unit, together with C1, R1,....
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This simple IR detector turns on a real LED when Q2 is exposed to invisible IR radiation found in fiber-optics systems, position sensors, and TV remote-control units. The device can be built on top of a 9V battery and held in place with RTV. Its power....
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This receiver is built around a uPC1373 IR remote-control preamplifier, a sensitive 30-to-40 kHz tuned detector, an automatic..
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Q3 is an IR phototransistor that responds to a modulated IR beam. Q1 amplifies the ac component of the IR beam. Q2 drives a ..
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This system contains an IR transmitter, an IR receiver/RF transmitter, and an RF receiver/alert beeper. Two IR ..
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An IR-sensitive phototransistor is used to sense soldering-iron temperature. The phototransistor must see t..
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The IR diode"s flash rate is determined by the value of CI, a 220-Â¥ capacitor that sets the rate of oscillation at 1 ..
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This circuit uses readily available parts to implement a 0-to-200-nA current source. The circuit borrows a PMOS ..
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The UHF motion detector operates on the Doppler radar principle. Ql is an oscillator that creates a radiated signal. An..
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If your ear is good, you can use this IR-pulse-to-audio converter to troubleshoot infrared remote-controls. It is also a good project for detecting infrared-light sources. A photo cell module (Radio Shack P/N 276-137) detects IR radiation and drives audio....
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Useful for A/B control, the IR receiver shown controls a relay from an infrared beam that has a pulsed tone-modulated signal. Ql is the photo receptor feeding op amp IC1, tone decoder IC2, and flip-flop IC3...
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The circuit operates from a 5-V supply arid has a current consumption of 2 mA. The output is a current source that drives or suppresses a current of more than 75 with a voltage swing of 4.5 V. The Q-killer circuit eliminates distortion of the output pulses....
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The transmitter for the wireless headphones is built around a CD4046 CMOS phase-locked loop, coupled with a driver transistor, and a pair of infrared LEDs. Although the CD4046 is comprised of two phase comparators, a voltage-controlled oscillator (or VCO),..
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The infrared remote-control tester uses a sensitive PN-type solar sensor that is connected directly to a Darlington amplifier made up of transistors Q1 and Q2. Biasing is provided by R1 and PI, a variable resistor that serves as a sensitivity control. The....
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In this strobe-light, two circuits are needed; one circuit charges a capacitor placing 320 V de between the cathode and anode of the flashtube. The other circuit provides bursts of approximately 4000 V to trigger the flashtube into conduction. The....
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This strobe gives a visual indication of a sensor input. The input signal causes Ul, a light dependent resistor, to chaijge CI..
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The circuit is activated by an LED/photoresistor isolator (Ul), which is a combination of a light-dependent resistor (LDR) and an LED in a single package. That device was chosen because of its high isolation (2000 V) characteristic, which is necessary....
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This strobe light operates from standard 120-Vac power. Rl limits the amount of current applied to the voltage doubler stage, which is comprised of CI, C2, C3, Dl, D2, C4, C5, and C6. Capacitors CI, C2, and C3 are connected in parallel and form a....
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The oscillator is a standard UHF design which delivers about 10 mW at 1.2 GHz. R1 and R2 bias the base of Q1 to 1.2 V via 12. Collector current is set by R3 to about 30 mA. C2 couples the base of Q1 to the stripline circuit. Tuning is provided by CVl, and....
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A typical circuit at 20 MHz is shown. The crystal, which has an internal series resistance Rs of 14ohm, oscillates at its third harmonic. The diode clamp Dl and D2 provides a constant amplitude control. ..
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The range of this transmitter is about 50 feet with a short whip antenna. The tone generator, is made up of a unijunction transistor, Q1, and R1, R2, R3, and C2. Transistor Q1 pulses on and off at a rate determined by the time constant of R1 and R2,....
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This VHF VCO circuit is suitable for 30 to 200 MHz. Q1 can be replaced by a 2N3563 for operation above 100 MHz..
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The MAR-x preamp shown will cover up to 1.5 or 2 GHz with the correct MAR-x IC. ATTN1 should be omitted for low noise-figure.appli cations. ATTN1 and ATTN2 provide a means of limiting possible termination range,..
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This application involves demodulation of a frequency-modulated subcarrier of the main channel. This popular example uses the PLL to recover the SCA (Subsidiary Carrier Authorization or storecast music) signal from the combined signal of many commercial FM....
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The internal zener on pin 15 of the 4046B supplies a stable voltage to the 3140IC op amp. This amplifier modulates the 4046B V..
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An LM311 comparator converts a small analog signal to a digital level for the DC4046 phase-locked loop, which is configured as a first-order FM demodulator. This demodulator works with a 50-kHz FM modulated input signal. It has applications in FM light beam....
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The FM modulator is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV-209, are used to frequency modulate the oscillator. The 5000- potentiometer is used to bias the varactors for best linearity. The output frequency of approximately 100....
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Op amp Ul and its associated components comprise the 67-kHz bandpass filter. A twin-T network, comprised of four 1100-12 resistors and four 0.0022- capacitors, is connected in the feedback network of the op amp. That gives some gain at 67 kHz and heavy....
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In microprocessor control of multiple loads, the minimum cost per load is critical. A typical application example is a large display involving driving arrays of incandescent lamps. This circuit provides minimal component cost per stage and optocoupler....
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This circuit operates from a 16- to 50-V supply. Adding the buffer circuit (within the dashed lines) offe..